Liquid crystal display (LCD) is widely applied for displaying apparatus such as a word processor, personal computer, television, monitor and mobile information terminal because the display can be operated with low voltage and low electric power consumption and directly connected to an IC circuit and can be made to a thin form. The LCD is basically constituted by, for example, a liquid crystal cell having polarizing plates on both sides thereof.
The polarizing plate is a plate capable of penetrating light polarized in a certain direction. Therefore, the LCD plays an important role for visualizing the variation in the stretching direction of the liquid crystal. Consequently, the properties of the LCD are largely depending on those of the polarizing plate. The polarizing plate is generally constituted by a polarizing film such as a poly(vinyl alcohol) film, on which iodine or a dye is adsorbed in an oriented state, and a transparent resin layer is laminated on both of the surfaces of the plate. For the transparent resin layer, cellulose ester film such as triacetyl cellulose film is frequently employed since such the film has low double refractive index and suitable for the protective film.
In recent years, the liquid crystal display is developed in place of CRT for a monitor having large image size and high image. quality. Requirements for the protective film for the polarizing plate of the liquid crystal display becomes severe. Particularly, there was a problem such that properties such as visibility and the like are easily fluctuated via fluctuation of optical characteristics when a cellulose ester film is installed in a liquid crystal display, since the cellulose ester film has a water-absorbing property. It is specifically demanded to improve retardation stability with respect to environmental-variations when the cellulose ester film is a support film used as an optical compensating film for enlarging a viewing angle.
On the other hand, a solution-casting method is commonly applied for producing the cellulose ester film; in such the method cellulose ester is dissolved in a solvent such as a halogenated solvent to prepare a solution so called to as dope, and the dope is cast on a rotating endless belt or drum as a metal support to form the film. After the casting, the film is solidified on the support by evaporation of a part of the solvent and peeled off from the support. After that, the remaining solvent is removed to obtain the cellulose ester film.
In such the method, however, massive cost is required for equipment such as a drying line and apparatuses for recovering and recycling the evaporated solvent, drying energy and production since the solvent remaining in the film should be removed. Therefore, the cost reducing causes a problem.
For dissolving such the problem, the optical film described in Patent Document 1, which is cellulose ester film form by a melt-casting method. Though optical films exhibiting good optical and physical properties accompanied with dimension stability may be obtained, stability in retardation variation against the environment is further demanded.
As to an optical compensating film, disclosed is a technique to provide an optical compensating film, to which a desired phase difference is added, by stretching the whole support at high temperature after coating a polymer layer having an optical compensating function on a support employing a triacetylcellulose film prepared as a support via solution-casting (refer to Patent Document 2, for example). However, the triacetylcellulose film which is a film prepared via solution-casting, and used as a polarizing protective film causes problems such that retardation unevenness caused by stretching unevenness-is easily generated in the case of stretching at high temperature after separately providing a polymer layer having an optical compensating function without using a preparation process. For this reason, demanded is an optical film in which transparency and flatness are not deterioratedeven though a stretching process for a support is carried out in high temperature treatment, and excellent retardation uniformity is exhibited.
It is also demanded to improve heat generation caused by a direct optical LED backlight as well as visibility variation depending on environmental variations, when the optical compensating film is installed in a liquid crystal display.    [Patent Document 1] Japanese Patent O.P.I. Publication No. 2000-352620    [Patent Document 2] Japanese Patent O.P.I. Publication No. 2004-4474